Cap-shaped control electrode securing cathode by thin supporting members



Nov. 21, 1967 CAP-SHAPED Filed 0012. 14, 1966 F. H. R. ALMER ETAL3,354,340 CONTROL ELECTRODE SECURING CATHODE BY THIN SUPPORTING MEMBERS2 Sheets-Sheet 1 VZ// /Ellll r, //%-21 1967 F. H. R. ALMER ETAL 3,35

CAP-SHAPED CONTROL ELECTRODE SECURING CATHODE BY THIN SUPPORTING MEMBERSFiled 001;. 14, 1966 2 Sheets-Sheet 2 Flu FIG. 3

INVENTORS ALMER FRIEDRICH H- R.

GERARDUS SM. SCHR IJNEMAKERS ADRIANUS KUIPER ALPHONSUS P. VAN ROOY AGENTUnited States Patent @hfice 3,354,340 Patented Nov. 21, 1967 3 354 340CAP-SHAPED CONTRUL ELECTRODE SECURING CATHODE BY THIN SUPPORTING MEMBERSFriedrich Hermann Raymund Aimer, Gerardus Servaas Marie Schrijnernakers,Adrianus Kuiper, and Alphonsus Petrus van Rooy, Emmasingel, Eindhoven,Netherlands, assiguors to North American Philips Company, Inc., NewYork, N.Y., a corporation of Delaware Filed Oct. 14, 1966, Ser. No.591,367 Claims priority, application Netherlands, Gct. 22, 1965,65-13,66S 14 Claims. (Cl. 313-82) ABSTRACT OF THE DISCLOSURE A quickheating narrow tolerance, easily manufactured electron source for acathode-ray tube comprising a perforated, cap-shaped control electrodein which a cylindrical cathode having an emissive end surface is securedby a plurality of thin supporting members, a supporting cylinder, anannular insulating body, and an annular metal body which is secured tothe cap-shaped control electrode.

This invention relates to an electron source for an electron gun,comprising a perforated, cap-shaped control electrode in which acylindrical cathode having an emissive end surface is secured by meansof a plurality of thin supporting members, a supporting cylinder, aninsulating body in the form of a cylindrical ring, and an annular metalbody which is secured to the control electrode. 7 Many constructions arealready known in which a cathode is suppOrted in an insulating body bymeans of a plurality of thin supporting members in the form of narrowstrips and a supporting cylinder, said insulating body being secured ina cap-shaped control electrode, possibly with the use of a supportingring which can be moved within the control electrode for adjusting thecorrect distance between cathode and control electrode and is thensecured to the control electrode. Frequent use is also made of partsexpanding in opposite directions, resulting in the distance betweencathode and control electrode being maintained constant independently ofvariations in the temperature of the cathode. However, these knownconstructions invariably have, in addition to cer tain advantages, insome respect one or more disadvantages.

A construction which is advantageous in every respect is obtained forsuch an electron gun comprising a perforated cap-shaped controlelectrode in which a cylindrical cathode having an emissive end surfaceis secured by means of a plurality of supporting members, a supportingcylinder, an insulating body in the form of a cylindrical ring, and anannular metal body which is secured to the control electrode if,according to the invention, the outer'cylindrical face of the insulatingbody is connected to the annular metal body and its inner cylindricalface is secured to the supporting cylinder by means of a substance fusedthereon, the ends of the supporting cylinder projecting from theinsulating body and the supporting members of the cathode being securedto the cathode support and to a flange provided on the end of thesupporting cylinder adjacent the emissive surface of the cathode, whilethe annular metal body also being secured to a plurality of tonguesrecessed in the cylindrical wall of the control electrode.

The insulating body may advantageously comprise a body of prepressedglass which may be secured by fusion to both the supporting cylinder andthe annular metal body. However, the connection to the metal ring ispreferably obtained by pressure-welding. The same may be the case withan insulator made of crystallized glass or fusible ceramic materialcomposed of, for example, a mixture of 50% by weight of A1 0 and 50% byweight of a mixture consisting of equal parts by weight of CaO and B203.

However, if the electron gun must be able to sustain a high degassingtemperature, the insulating ring will have to be made of crystallizedglass or ceramic material. The said construction affords the advantagethat the cylindrical faces only of the ceramic insulator and hence notpart of its upper and/ or lower surfaces must be metallized forsoldering said faces to the supporting cylinder and the metal ringrespectively. The end-faces of the insulating ring may be deprived ofany metal deposited thereon by merely grinding it flat. A plurality ofsupporting rods for securing the heating body may be sealed or solderedin the insulating ring.

The invention will now be described with reference to the accompanyingdrawings, in which:

FIGURE 1 is a sectional view of one embodiment of an electron sourceaccording to the invention;

FIGURE 2 shows another embodiment of a cathode construction according tothe invention;

FIGURE 3 shows another mode of connection of the insulator and thesupporting cylinder, and

FIGURE 4 is a developed view of the material forming the controlelectrode.

In FIGURE 1, reference numeral 1 indicates the cathode Which is securedin a cap-like control electrode 2 by means of three thin supportingstrips 3 welded to a flange 14 of a supporting cylinder 4. Thesupporting cylinder 4 is sealed in an insulating cylindrical ring 5, thecylindrical outer face of which is connected, by fusion or by so-calledpressure-welding to an annular metal body 6, which, following theadjustment of the correct distance of cathode 1 relative to controlelectrode 2, is Welded to strips 7, recessed in a cylindrical side-wall18 of control electrode 2. The said cathode-control electrode distanceis preferably adjusted by adjusting the capacitance of cathode 1relative to a first anode 21, as is known per se.

The shielding of the cathode relative to the first anode which is thusrequired is obtained by clamping the ring 6 on a welding electrode (notshown) which is formed as a hollow cylinder housing the insulatedresilient member which may make contact with the lower end of supportingcylinder 4. The correct cathode to control electrode distance isadjusted by displacing the electron gun relative to the cathode 1.Subsequently the ring 6 is welded to the strips 7. Since the strips 7are slightly resilient the distance between the cathode 1 and thecontrol electrode 2 is prevented from being influenced during thewelding operation.

The cathode 1 has a cap-like support, the emissive layer being presenton the closed end surface. The support comprises a cathode cylinder 8which serves as an envelope for a heating body 9. However, the cathodecylinder 8 does not serve as a structural element, since the supportingstrips 3 of the cathode are Welded to the cathode support 4 itself. Thecathode cylinder 8 may therefore be made of thin material so that theheat content may be small and a short heating-up time is obtained. Thisis especially true if the heating element is substantially concentratedadjacent the closed end of the cathode and hence near its emissivesurface, in which event a very small wall thickness (even less than 25p)may be used since the heat conduction of the cylinder is then lessimportant.

However, due to the small dimensions of the cathode a 1, it is ingeneral impossible for the heating element to be arranged entirelywithin the cathode cap, although the construction of the heating elementmay be such that most of the heat is evolved close to the emissivelayer.

Since the length of the cathode cylinder 8 has no function at all, instructural respect it may be varied so that different heating energiescan be used. In fact, the cathode cylinder has the task not only toenvelop the heating element, but also to reduce the heating-up time ofthe cathode, the cathode reaching its emission temperature when theheating element is concentrated in it, much sooner than the cylinder 8which then receives its heat substantially through conduction from thecathode support 1. After the cathode is already emitting electrons thetemperature of cylinder 8 increases so that the radiation towards thesupporting cylinder 4 increases and hence the thermal losses increaseand excessive heating of the cathode is avoided.

An even shorter heating-up time of the emissive layer may be obtained byreducing the length and hence the mass of the cathode support, as shownin FIGURE 2. However, the radiating surface thus becomes too small forpreventing excessive heating of the cathode. This may be compensated forby blackening the outer surface of cathode cylinder 8 and possibly alsoof cathode support 1, so that eventually the same amount of energy isradiated. In this case, preferably the inner side of supporting cylinder4 is also blackened.

In order to retard the thermal conduction from the cathode 1 to thecylinder 8, the cathode cylinder 8 within the supporting cap emergesinto at least two, preferably three, narrow tongues the ends of whichare secured by welding, at 20, inside the. cathode support 1 closelybelow the upper face thereof. Consequently, a larger part of the innersurface of cathode support 1 is radiated directly by the heating body 9,while the tongues of the cathode cylinder are also warmed up, resultingin the heat dissipation from the support 1 through the welding areas ofsaid tongues to the part of cathode cylinder 8 projecting below thecathode being retarded. Thus, the emissive end surface of the cathodesoon reaches the operating temperature.

The open end of the cathode support 1 is provided with a flange forobtaining greater rigidity. Furthermore, the supporting strips 3 of thecathode may be welded to the said cathode flange. It has been foundthat, if the angle made by the strips 3 with the surface of a flange 14on supporting cylinder 4 is chosen suitably, also in connection with thecoefficients of thermal expansion of the cathode support 1, the controlelectrode 2, the strips 3 and the supporting cylinder 4, not only thedisplacement of the emissive surface relative to the control electrode 2can be maintained very small in a large range of differenttemperaturesfbut also the influence of the mechanical tolerances in themanufacture of these various parts exerted on the cathode-to-controlelectrode distance may, be reduced substantially to zero. The optimumangle will generally be comprised between and 60. The strips 3 must thenbe formed so that they can bend during the heating-up of the cathode andwith strong variations in temperature, only near the points of bendingadjacent the flanges to which they are secured. To this end, the stripsare strengthened, between their points of bending by meansof impressedgrooves or the like.

The strips 3 may alternatively have the form of thin rods depressedslightly at the points of bending in order to reduce the rigidity atthese areas so thatbending during the expansion of the various componentparts will occur in situ.

To reduce as far as possible the dissipation of heat from the cathode 1,through the supporting member 3 the latter are made of hard material,such as nickel-iron and nickel-iron-molybdenum compounds, so that theycan be thin while having the required strength.

Since the cathode-to-control electrode distance in an electron source ofthe described composition remains substantially constant, the saiddistance may be made very small without the cathode being liable tocontact the control electrode during the rapid and strong heating on de'gassing the electrodes in the cathode-ray tube.

The heat radiated by the cathode cylinder 8 is collected and reflectedby the supporting cylinder 4 which reaches a comparatively hightemperature. The cylinder 4 may consist of an alloy of a low coefficientof, expansion, such as fernico, which can be sealed in glass and is alsoa comparatively poor thermal conductor. Since the cylinder 4 contactsthe insulating ring 5 only over a small part of its length, thedissipation of heat to the insulating material maybe small. If desired,the heat con duction may be reduced further by means of recesses in theannular inner surface of the insulator 5 so that it is not connected tothe supporting cylinder 4 throughout its periphery, as shown in FIGURE3. Due to the poor heat conduction of the material forming the cylinder4, the end 15 thereof which projects from the insulator 5 assumes a hightemperature owing to the heat radiation from the cathode 1, so that thesupporting members 3 cause only a low thermal loss.

The supporting cylinder 4 also acts as a screen for metal vapour whichmight deposit from the cathode 1 and the cathode cylinder 8 onto theinsulator 5. Furthermore, the supporting cylinder 4 ensures that duringthe final assembly, that is during all the remaining assemblingoperations on the electron gun after the ring 6 has been secured to thecontrol electrode 2, the cathode cylinder 8 is not touched which wouldinvolve the risk that the adjustment of the cathode might be modified.

In the insulating ring 5 there are sealed or soldered two supportingrods 10 to which a fastening clasp 11 for the heating-wire ends of aheating element 9 is secured, the said fastening clasp being dividedlater by cutting away a portion 11. The clasp 11 substantially has theshape of an M the limbs of which become aligned with the supporting rods10 so that the clasp 11 may be wholly enclosed in the above-describedhollow welding electrode during the ca pacitive adjustment of thecathode-to-control electrode distance. After the electron source ismounted in an electron gun, the parts of the clasp 11 are welded throughthe tongues 12 to current-supply pins sealed in a base part. The tongues12 may be bent over, if necessary, without the adjustment of the heatingbody in the cathode being influenced thereby. The supporting cylinder 4is provided with a current supply conductor 13 for the cathode.

Since the insulating body 5 is connected to the supporting cylinder 4 byusing a fused substance, the thermal contact obtained is reproducible sothat little differences in the temperatures of different cathodes occur.This is also the case if the insulating part 5 is made of ceramicmaterial since the connection to the metal cylinder 4 is then obtained:by soldering. Also, the dissipation of heat from the insulating body 5through a pressure weld to the annular body 6 is satisfactorilyreproducible.

The control electrode 2 may be manufactured in a very simple manner froma metal plate shaped into the form shown in FIGURE 4. When this plate ispushed through a cylindrical template, a cap-shaped electrode resultshaving its cylindrical side-wall formed by parts 18 and the tongues 7.

The invention providesan electron source for an electron gun which mayhave a very small working distance between cathode and controlelectrode, which has a very stable operation independent of variationsin temperature, which is mechanically rigid and resistant to shocks,which has a very low tendency to cause microphonic interference andwhich can be manufactured in a very simple manner and at low cost sincemechanical tolerances exert only small influence on the adjustment.

What is claimed is:

1. An electron source for an electron gun, comprising a perforated,cap-shaped control electrode in which a cylindrical cathode having anemissive end surface is secured by means of a plurality of thinsupporting members, a supporting cylinder, an insulating body in theform of a cylindrical ring, and an annular metal body which is securedto the control electrode, characterized in that the outer cylindricalface of the insulating body is connected to the annular metal body andits inner cylindrical face is secured to the supporting cylinder bymeans of a substance fused thereon, the ends of the supporting cylinderprojecting from the insulating body and the supporting members of thecathode being secured to the cathode support and to a flange provided onthe end of the supporting cylinder adjacent the emissive surface of thecathode, while the annular metal body being secured to a plurality oftongues recessed in the cylindrical Wall of the control electrode.

2. An electron source as claimed in claim 1, characterized in that theinsulating body consists of glass and is fused at least with thesupporting cylinder and connected to the annular metallic body.

3. An electron source as claimed in claim 1 characterized in that theinsulating body consists of crystallized glass.

4. An electron source as claimed in claim 1, characterized in that theinsulating body consists of fusible ceramic material and is fused atleast with the supporting cylinder and connected to the annular metallicbody.

5. An electron source as claimed in claim 4, characterized in that theinsulating body is of ceramic material, its cylindrical side faces beingmetallized and connected by means of solder to the supporting cylinder.

6. An electron source as claimed in claim 1 characterized in that theinner annular surface of the insulating body is provided with recesses,so that the said surface is secured to he supporting cylinder only overpart of the periphery thereof.

7. An electron source as claimed in claim 1 characterized in that aplurality of supporting rods for the ends of the heating wire aresecured in the insulating body.

8. An electron source as claimed in claim 7, characterized in that theheating body is connected to the sup- 6 porting rods by means of aninitially M-shaped clasp the limbs of which are aligned with thesupporting rods, the clasp being divided into two parts by removal ofits central piece.

9. An electron source as claimed in claim 1 characterized in that thetwo ends of the supporting cylinder project from the insulating body,the end of the supporting cylinder adjacent the emissive surface of thecathode being provided with a flange to which the ends of the supportingmembers of the cathode are welded.

10. An electron source as claimed in claim 1 characterized in that thesupporting members of the cathode are secured to a flange on the openend of the cap-shaped cathode support itself.

11. An electron source as claimed in claim 1 characterized in that thecathode cylinder inside the cap-shaped cathode support merges into atleast two tongues the ends of which are welded to the inner surface ofthe said sup port, the heating element being concentrated substantiallynear the closed end of the cathode.

12. An electron source as claimed in claim 1 characterized in that thewall thickness of the cathode cylinder is less than 25 1, the heatingelement being concentrated substantially near the closed end of thecathode.

13. An electron source as claimed in claim 1 characterized in that atleast one of the outer surfaces of the cathode cylinder, of the cathodesupport and the inner surface of the supporting cylinder are blackened.

14. An electron source as claimed in claim 1 characterized in that theannular metallic :body is welded to tongues formed in the cylindricalside-wall of the cupshaped control electrode.

References Cited UNITED STATES PATENTS 2,833,952 5/1958 Hemphill et al.313-82 X 3,155,865 11/1964 Ney 31382 X ROBERT SEGAL, Primary Examiner.

1. AN ELECTRON SOURCE FOR AN ELECTRON GUN, COMPRISING A PERFORATED,CAP-SHAPED CONTROL ELECTRODE IN WHICH A CYLINDRICAL CATHODE HAVING ANEMISSIVE END SURFACE IS SECURED BY MEANS OF A PLURALITY OF THINSUPPORTING MEMBERS, A SUPPORTING CYLINDER, AN INSULATING BODY IN THEFROM OF A CYLINDRICAL RING, AND AN ANNULAR METAL BODY WHICH IS SECUREDTO THE CONTROL ELECTRODE, CHARACTERIZED IN THAT THE OUTER CYLINDRICALFACE OF THE INSULATING BODY IS CONNECTED TO THE ANNULAR METAL BODY ANDITS INNER CYLINDRICAL FACE IS SECURED TO THE SUPPORTING CYLINDER BYMEANS OF A SUBSTANCE FUSED THEREON, THE ENDS OF THE SUPPORTING MEMBERSING FROM THE INSULATING BODY AND THE SUPPORTING CYLINDER OF THE CAHTODEBEING SECURED TO THE CATHODE SUPPORT AND TO A FLANGE PROVIDED ON THE ENDOF THE SUPPORTING CYLINDER ADJACENT THE EMISSIVE SURFACE OF THE CATHODE,WHILE THE ANNULAR METAL BODY BEING SECURED TO A PLURALITY OF TONGUESRECESSED IN THE CYLINDRICAL WALL OF THE CONTROL ELECTRODE.